1. Technical Field
The present invention relates to a differential pressure valve unit that is accommodated in a liquid cartridge main body. In particular, the present invention relates to a structure of a differential pressure valve unit that is mounted to an ink cartridge used for an ink jet recording apparatus.
2. Related Art
In an ink jet recording apparatus, an ink cartridge that contains ink is mounted on a holder of the ink jet recording apparatus, and ink is supplied to a recording head.
In such an ink cartridge, a differential pressure valve unit having a valve member that is opened when a predetermined pressure difference between an ink containing portion containing ink and an ink supply portion supplying ink occurs is attached to the ink cartridge. Moreover, the ink cartridge described herein is an example of a liquid cartridge.
For example, a differential pressure valve unit described in Patent Document 1 has a valve member that can be elastically deformed on the basis of a pressure difference and has a cylindrical edge portion, a valve lid that has a valve member holding portion, substantially having a cylindrical shape, inserted into the edge portion of the valve member to fix the edge portion, and an urging member that is interposed between the valve member and the valve lid and urges the valve member in a direction away from the valve lid.
Patent Document 1: JP-A-2004-237720
In the above-described differential pressure valve unit of the ink cartridge, since the differential pressure valve does not normally operate when a downstream pressure chamber between a membrane valve serving as the valve member and the valve lid is empty, an ink end may be judged in a state where ink remains in the downstream pressure chamber. In a known differential pressure valve unit, a space of the downstream pressure chamber is comparatively large and, when the ink end is judged, a large amount of ink remains in the downstream pressure chamber.
In order to solve this problem, a method that makes the space of the downstream pressure chamber between the membrane valve and the valve lid small is considered. However, when the space of the downstream pressure chamber is made small, the flow of the liquid when the liquid is discharged from the chamber deteriorates, and thus responsibility to a pressure applied to the differential pressure valve unit may be degraded.